Magnetic induction heating is based upon transformer theory. Basically, a coil is located beneath the cooktop surface and is used to generate an oscillating, circular magnetic field. When an iron-based pot or pan is placed in the magnetic field, it acts as a shorted transformer secondary which is subject to a high induction current at low voltage. The cookware heats up and cooks its contents in the same manner as conventional ranges and cooktops. It is, however, the heat from the utensil that cooks the food, not the induction field, since heat is generated in the utensil which itself becomes the burner. The utensil will in turn heat the surface on which it is located but the area surrounding the utensil will remain cool.
The circuitry for a magnetic induction unit includes the induction coil which is generally of a flat, spiral configuration. An inverter is used to generate an oscillatory magnetic field in the 25-30 kHz range and, because of the fast switching, a semiconductor is used as the inverter switch. Since the inverter can be supplying 15 amperes at 30 kHz, it is necessary to cool the circuitry to prevent overheating of the components. In some ranges forced ventilation is present and may be used to cool the circuitry as well as to perform its other functions. In a convertible cooktop range, even those with a proximity ventilation system (i.e. where the range structure is combined with an exhaust system in proximity to the cooking surface), there is no provision for the internal cooling or ventilating of a cooktop cartridge, and therefore, such systems have not heretofore been designed or intended to have such a function. Their basic function has been to capture cooking fumes from utensils, grills or other cooking accessories at a point near the cooking surface and to direct these to the outdoors or through a filter with the capacity and ability to have a cleaning effect on the soiled air before returning it to the environment of the range.